1. Field of the Invention
The present invention relates to drum surface scanners and methods for plate size check and, more specifically to, in a drum surface scanner in which a plate positioned by a hole punch unit and then attached to a recording drum is exposed by means of light beam scanning, a mechanism for conveying the plate to the hole punch unit and the recording drum, and a method for plate size check employed by the mechanism.
2. Related Art Statement
Color printouts require an exposure process, a printing process, and several others before completion. Prior to the exposure process, an original image for color printing is separated into several colors, typically four colors of Y (yellow), M (magenta), C (cyan), and K (black), and image data is generated for each of the resulting colors. The resulting image data is provided to a drum surface scanner for use in the exposure process. The drum surface scanner includes a recording drum, around which a sheet plate is installed. The sheet plate is exemplified by a presensitized plate (PS plate), which is made of aluminum, plastic, paper, and others, previously coated with a photosensitive coating.
In the exposure process, based on the provided image data, the drum surface scanner exposes the plate installed around the recording drum for image printing thereon for each color as a result of color separation. That is, in a case where an original image is separated into four colors of YMCK, four images differing in color are each printed onto a plate, i.e., four plates in total.
In the printing process, used is a printer of a type applying inks corresponding in color to the image-printed plates to produce multi-colored printouts. At printing, if image shifting occurs to the plates printed with each different colored image, the resulting color printouts will be poor in quality. In order to prevent such image shifting, the plates usually each have punched holes at predetermined positions to use as a basis for position setting at printing. These punched holes are also used as a basis for image printing onto plates. Thus, a hole punch unit for forming such punched holes is provided to the drum surface scanner. With the aid of such punched holes, the drum surface scanner becomes free from image shifting occurring to plates, leading to high-quality color printouts provided by the printer.
Such a conventional drum surface scanner is disclosed in Japanese Patent Laid-Open Publication No. 2000-56467. As to the disclosed drum surface scanner, only its plate conveyor mechanism having relevance to the present invention is described briefly below.
FIG. 20 is an exploded view showing the structure of the conventional drum surface scanner. In the conventional drum surface scanner, an almost parallelepiped-shaped frame 1 is attached with a conveyor mechanism 2, a drive mechanism 3, a hole punch unit 4, a recording drum 5, and others. The drive mechanism 3 is not shown in FIG. 20 to avoid impairing clarity. FIG. 21 is a cross-sectional view of the main part of the conveyor mechanism 2, cut along a line A-A′ and viewed from the direction of an arrow B of FIG. 20.
In FIGS. 20 and 21, the conveyor mechanism 2 includes a lower tray 22, an upper tray 23, feed rollers 24, a conveyor roller 25 for plate loading, and a conveyor roller 26 for plate unloading. The lower tray 22 and the upper tray 23 are held securely in position to be a single piece between two side panels 21. The feed roller 24, and the conveyor rollers 25 and 26 are all rotatable, and also held securely in position between the two side panels 21. The feed roller 24 is used to convey plates placed on the lower tray 22 in the direction of the conveyor roller 25. The conveyor roller 25 is configured by two rollers, those of which are so arranged as to abut each other at the tip of the lower tray 22. Similarly, the conveyor roller 26 is also configured by two rollers, those of which are so arranged as to abut each other at the tip of the upper tray 23. The conveyor roller 25 and the feed roller 24 are each coupled, through a belt (not shown), with a motor M50 which is securely fixed to both of the side panels 21. The motor M50 drives both the conveyor roller 25 and the feed roller 24 into rotation. The conveyor roller 26 is coupled with, through another belt (not shown), a motor M54 which is also securely fixed to both of the side panels 21. The motor M54 drives the conveyor roller 26 into rotation.
The lower and upper trays 22 and 23 are provided, respectively, with small holes 27 and 28, and directly therebelow, sensors PH50 and PH54 are each affixed. These sensors PH50 and PH54 are used to detect whether there is any plate placed directly above the small holes 27 and 28, respectively.
The conveyor mechanism 2 structured as such is securely placed onto the upper part of the frame 1, as indicated by a one-dot arrowed line α in FIG. 20. Here, the conveyor mechanism 2 rotates at a predetermined angle about a rotary shaft 29 protruding outwardly from those two side panels 21 (see an arrow β in FIGS. 20 and 21).
The drive mechanism 3 is incorporated to rotate the conveyor mechanism 2 as such. FIG. 22 shows the drive mechanism 3 viewed from the direction of an arrow C shown in FIG. 20.
In FIG. 22, the drive mechanism 3 includes, two of each, a cum follower guide 31, a motor M55, a cum gear 32, and a cam follower 33. The drive mechanism 3 also includes, at least one of each, a sensor detection panel 34, a sensor PH55, and a sensor PH56.
The cum follower guides 31 each have a parallelepiped shape, and an oval-shaped through hole is formed therein. The cum follower guides 31 are fixedly attached to the side panels 21, respectively, such that the through holes are faced to each other via the conveyor mechanism 2. The motors M55 are placed proximal to the side panels 21, respectively, to face each other via the conveyor mechanism 2, and fixed to the frame 1. The cum gears 32 are also fixed to the frame 1 in such a manner as to face to each corresponding side panel 21. Here, the cum gears 32 are each driven by the corresponding motor M55 into rotation about their own shafts. The cum followers 33 are fixed, respectively, in such a position as to move in a circle, around the shaft of the corresponding cum gear 32, on the outer parts of one plane of the cum gear 32, i.e., the plane facing to the corresponding side panel 21. The cum follower 33 is disk-shaped, a diameter of which is almost the same as the narrower diameter of the through hole of the cum follower guide 31, and thus perfectly fits in the through hole. With such a structure, the cum follower 33 couples together the cum follower guide 31 and the gum gear 32, so that the conveyor mechanism 2 is supported by the drive mechanism 3. The disk-shaped sensor detection panel 34 is placed concentrically around the corresponding cum gear 32, and rotates together therewith. The sensor detection panel 34 has a slit 35 formed in the outer parts thereof. In order to detect the slit 35 in the rotating sensor detection panel 34, the sensors PH55 and PH56 are securely fixed to the frame 1.
With such a structure, the sensors PH55 and PH56 both become able to detect the slit 35 which does not stay at the same position, and the drive mechanism 3 moves and stops the conveyor mechanism 2 to/at its upper and lower positions.
Described next is the hole punch unit 4 of FIG. 20. FIG. 23 shows a cross-sectional view of the hole punch unit 4, cut along a line E-E′ and viewed from the direction of an arrow F of FIG. 20.
In FIG. 20, the hole punch unit 4 includes at least two punchers 41, and a mounting member 42. The punchers 41 each mainly include, as shown in FIG. 23, a main body 43, a sensor PH62, a motor M60, and a punch 44. The main body 43 has a gap 45, into which a plate coming over a first supply pass line (will be described later) is inserted. The sensor PH62 detects plate insertion into the gap 45. Once the sensor PH62 detects plate insertion, the motor M60 starts driving. With the aid of a cum mechanism (not shown) in the main body, the driving power eventually moves the punch 44 up and down. As the punch 44 moves up and down responding to the power provided by the cum mechanism, the plate inserted in the gap 45 is punched in. As such, the resulting plate has punched holes and/or cuts formed at one end thereof. The mounting member 42 has a parallelepiped shape, and a gutter 46 is formed along the longitudinal direction thereof. To the gutter 46, the corresponding puncher 41 is attached. Such a hole punch unit 4 is securely fixed onto the frame 1 as indicated by a one-dot arrowed line 6 shown in FIG. 20.
Described next is a recording drum 5 shown in FIG. 20. FIG. 24 shows the recording drum 5 and components locating proximal thereto, cut along a line G-G′ and viewed from the direction of an arrow H of FIG. 20.
In FIGS. 20 and 24, the recording drum 5 is placed within the frame 1, specifically, in such a position diagonally below the conveyor mechanism 2 and the hole punch unit 4. The recording drum 5 has an almost cylindrical shape, and rotates about its own shaft responding to the driving power coming from a motor M1. To the outer surface (annular surface) of the recording drum 5, a plate P (see a shaded part of FIG. 20) coming over a second supply pass line (will be described later) is installed therearound. Further, the drum surface scanner includes, for the purpose of securely place the plate P on the recording drum 5, at least two positioning pins 51, a head clamp 52, and a tail clamp 53. As shown in FIG. 20, these positioning pins 51 are securely affixed onto the outer surface of the recording drum 5 so as to be aligned parallel to the center axis thereof. Thereby, the positioning pins 51 can clamp one end of the plate coming over the second supply pass line.
Next, referring to FIGS. 25 to 33, a sequence of processes executed by the components described in the foregoing will be described in detail.
First, the plate P is provided to the lower tray 22 of the conveyor mechanism 2 (see FIG. 25). This plate supply is done manually by operators, or automatically by an automatic plate supply mechanism (not shown) additionally provided to the drum surface scanner. Once the sensor PH50 detects that the plate P has been supplied, the conveyor mechanism 2 moves the lower tray 22 to its upper position for a punching process. As a result, the conveyor roller 25 of the conveyor mechanism 2 and the gap 45 of the hole punch unit 4 are aligned straight, so that the first supply pass line as indicated by a two-dot arrowed line η is formed therebetween (see FIG. 26). Then, the feed roller 24 and the conveyor roller 25 rotate (positive rotation) in such a direction that the plate P moves from the conveyor mechanism 2 towards the hole punch unit 4 (see an arrow θ). With such a rotation, the plate P is conveyed over the lower tray 22 to the first supply pass line (see FIG. 27). Here, on the way in the first supply pass line, the plate P is adjusted in position with respect to the punchers 41 by a centering mechanism, which is not shown. As a result of position adjustment, the plate P preferably has two punched holes and/or cuts formed symmetrically with respect to the center line thereof. The resulting plate P after position adjustment is then guided to the gap 45 of the corresponding puncher 41.
In the hole punch unit 4, if the sensor PH62 of the corresponding puncher 41 detects that one end of the plate P has reached thereto, the plate P is formed with punched holes and/or cuts at predetermined positions thereof. Here, in the case with cuts, those are formed in the same shape at the same pitch as the positioning pins 51 which are securely affixed onto the recording drum 5. In the case with punched holes, those are formed in the same shape at the same pitch as pins provided to a printer (not shown) which is used in the printing process.
After the punching process, the feed roller 24 and the conveyor roller 25 rotate (negative rotation) in a direction from the hole punch unit 4 to the conveyor mechanism 2 (see an arrow ι) at, almost, a constant speed. As a result, the punched plate P moves backward over the first supply pass line to be on the lower tray 22 again (see FIG. 28). In response to such a movement of the punched plate P, the conveyor mechanism 2 moves the lower tray 22 to its lower position to have it face to the recording drum 5, i.e., to have the line extended straight from the conveyor roller 25 abut the outer surface of the recording drum 5 (see FIG. 29). In this manner, the second supply pass line is established between the conveyor roller 25 and the recording drum 5. Then, the feed roller 24 and the conveyor roller 25 rotate positively to forward the punched plate P from the lower tray 22 onto the second supply pass line in the direction of the recording drum 5 (see an arrow λ). The forwarded plate P is then defined by position with respect to the recording drum 5 by the cuts formed at one end as fitting into the positioning pins 51.
Thereafter, a first clamp drive (not shown) drives the head clamp 52 to clamp one end of the plate P. In response, the recording drum 5 rotates (positive rotation) in a direction indicated by an arrow μ of FIG. 30. As a result, the plate P is wound around the recording drum 5 while being ejected from the lower tray 22 (see FIG. 31).
After the exposure process to the plate P, the exposed plate P installed around the recording drum 5 is unloaded as below.
The recording drum 5 rotates in an opposite direction (negative rotation) to unload the plate P to the conveyor roller 26 through an ejection pass line which is indicated by a two-dot arrowed line ρ in FIG. 32. The conveyor roller 26 then rotates in the direction indicated by an arrow τ in FIG. 33, i.e., such a direction that the plate P coming over the ejection pass line is moved to the upper tray 23. As a result, the plate P is provided onto the upper tray 23 (FIG. 33).
The issue here is that such a conventional drum surface scanner bears the following problems. First, plate conveyance to the hole punch unit 4 and the recording drum 5 is dependent only on the movement of the feed roller 24 and the conveyor roller 25.
Therefore, if the feed roller 24 and the conveyor roller 25 get dirty and thus reduced in their conveyance capabilities, for example, plate conveyance may not be completed to the predetermined position of the corresponding puncher 41, specifically, until the plate perfectly fits in the gap 45. If this is the case, without position adjustment, the plate may be formed with punched holes and/or cuts. It should be noted here that the sensor PH62 provided to each puncher 41 merely detects plate insertion into the gap 45, and thus is not capable of detecting whether the plate has been correctly positioned.
Moreover, problematically, the plate is not completely conveyed until its cuts abut the positioning pins 51 of the recording drum 5. As a result, the plate is clamped without correctly defined by position, and the exposure process get started.
There is another problem about plate size in the conventional drum surface scanner. In detail, plates used in the drum surface scanner vary in size, and thus settings are accordingly made to the scanner depending on what plate size is to be applied thereto. The scanner follows the settings for a sequence of processes. However, this does not always work appropriately if plate supply is made manually by operators, possibly resulting in mistakes such that the plate supplied to the lower tray 22 of the conveyor mechanism 2 will be wrong in size, different from the previously-made settings. The conventional drum surface scanner detects the plate size to prevent mistakes of the type, but such detection is not enough.
The reason is that, in the conventional drum surface scanner, plate size detection is not made at once. In detail, with respect to the heading direction of the plate, the width X of the plate is detected at the time of centering process in the hole punch unit 4, while the length Y of the plate is detected at the time of conveyance to the recording drum 5, i.e., calculated from the rotation amount of the recording drum 5 when the tail end of the plate is detected. Accordingly, if the plate wrong in length Y is supplied to the lower tray 22, the plate resultantly goes all the way to the recording drum 5.